1. Field of the Invention
The present invention relates to a method for extracting crude oil from a reservoir. More particularly, it relates to a method for extracting crude oil from a reservoir in situ.
2. Description of the Prior Art
Vast quantities of crude oil reserves are to be found in reservoirs which do not permit oil extraction by the conventional methods. These crude oil reservoirs may be in the form of viscous tar sands whose available oil adheres to or between the sand particles and may not be pumped.
Another type of reservoir is a heavy viscous oil, or bitumen, reservoir. In such a reservoir, the bitumen is too viscous to be pumped by conventional pumping equipment.
Various attempts have been made to extract such crude oil in an economical manner. Such attempts have utilized, for example, the addition of wetting agents, surfactants, steam, water at elevated temperatures, micellar dispersions or in situ combustion. However, these prior art methods have recovered very small amounts of the in-place fluid and in some cases required that the reservoir material be extracted prior to the extraction of the crude oil.
Known extraction methods include open pit or strip mining and, in the case where the reservoir is covered with a thick overburden, underground mining of the sand or bitumen. However, such methods are uneconomical and environmentally unsound. Pit and strip mining require the removal of the overburden which requires subsequent land reclamation while extensive underground mining is expensive and weakens the covering overburden.
Applicants are aware of one oil sand extraction method, described in U.S. Pat. No. 1,651,311 to Atkinson, which attempts to extract crude oil without the prior extraction of the entire reservoir material, that is, in situ. In Atkinson, oil sand that has been naturally flooded with water is saturated with a strong alikali, such as soda ash, caustic soda or caustic potash, at ordinary temperatures. According to Atkinson, the alkali is introduced through existing well holes and overcomes the capillary, adhesive and viscous tendancies of the crude oil so that it separates from the sand. The crude oil then rises to the top of the already flooded wells and is removed.
However, Atkinson has several shortcomings. First, it requires large amounts of alkali. Second, it may only be used in already flooded wells. Finally, the alkali does not efficiently separate the crude oil from the sand.